DE102007050010A1 - Method and apparatus for producing silicon - Google Patents

Abstract

The present invention relates to a process for the production of ultrapure silicon from, for example, optionally doped quartz sand by thermal reduction in a microwave oven.

Description

The The present invention relates to a method for producing silicon. in particular of high-purity silicon, as is the case for the production of semiconductors and solar cells needed as well as a device for this.

For the application In these areas silicon is needed, its degree of contamination is extremely low or precisely controlled.

moreover the manufacturing process should be cost effective.

It Various methods for producing high-purity silicon are known.

To One approach is metallurgical silicon as the starting material used, which is obtained from quartz sand in a blast furnace process. The metallurgical silicon is then over a multi-stage on Trichlorosilane-based process to polycrystalline ultrapure silicon implemented. Here, the metallurgical silicon with silicon tetrachloride and hydrogen converted to trichlorosilane and from the trichlorosilane obtained by disproportionation of silane tetrachloride and silane. From the silane formed is then by thermal decomposition silicon rods Reinstsilizium won.

According to one Another approach is silicon from quartz or quartz glass by reduction receive.

One Example for this is the so-called carbothermic reduction, where carbon is used as a reducing agent. Common is the reductive Process that melted the starting material for the reaction must be what an energy-intensive process is.

So is known to perform the melting in an electric arc furnace. From The disadvantage here is that the electrodes used in an electric arc furnace subject to wear and also the risk of contamination of the electrodes by the Reducing agent, such as carbon exists.

It There was therefore a need for a method according to which silicon from an easily accessible Raw material obtained in a simple manner and energy favorably can be.

The inventive method based on the second approach, which is based on the reductive extraction based on silicon.

According to the invention is a Process for the preparation of silicon by reductive conversion of a Silica-based feedstock with a reducing agent provided, wherein the starting material based on silica reacted together with the reducing agent in a microwave oven become.

The used according to the invention Silica-based raw material can be quartz sand, quartz or glass.

The glass may be quartz glass, ie a glass of 100% SiO ₂ , or quartz glass, to which suitable doping elements have been added as required. Advantageously, if possible, a starting material is used whose composition corresponds to the requirements of the later application, for example with respect to the type and amount of the doping elements. As a result, the expense of possibly required purification of the resulting silicon can be avoided or at least reduced.

For the inventive method the starting material is crushed silica-based and used for example in powder form. A suitable powdery starting material is for example quartz flour.

For the reduction For example, a reducing agent can be used as it is for the preparation of silicon by thermal reduction is known.

Examples therefor are carbon based reducing agents like carbon powder, Graphite powder or a mixture of carbon powder and graphite powder, or aluminum, magnesium etc.

According to the invention preferred the reduction takes place carbothermally, that is with reducing agents Carbon-based.

Warming in A microwave oven is made by exciting the to be heated Materials with electromagnetic radiation.

For this is the mixture of starting material and reducing agent in one suitable reaction vessel where. This reaction vessel can consist of a material that is used for the working frequency of Microwave ovens is transparent.

Alternatively, a container may be used which consists of a material which is not or only partially transparent to the operating frequency of the microwave oven used. In this case, the container is also heated, so that the heating and the melting by heat conduction from the container material in the reacted Mixture is supported.

The container material is therefore not critical, as long as it is transparent to the microwaves is or by heat conduction the necessary warming enables the mixture to be reacted.

advantageously, can for the inventive method Microwave ovens are used, which work with a frequency as for standard household Microwave ovens is used. These use electromagnetic Radiation with a frequency of typically around 2.455 GHz.

There according to the invention in principle Microwave ovens can be used, as they are commercially available at low cost, the process of the invention is characterized in particular by a simple apparatus handling.

Preferably microwave ovens are used, which have a power control, In particular, have a continuous power control, so that, for example, the irradiation of microwaves as needed can be adjusted and regulated.

Of the Use of power controlled microwave ovens is another Contribution to energy saving.

to Preparation of the silicon is the starting material based on silica crushed small and mixed with the reducing agent.

The The mixture obtained is placed in a container and the starting material Silica-based is heated by the action of microwaves and melted, wherein the reduction is carried out by the reducing agent.

The Reaction is preferably carried out under an inert gas atmosphere, for For example, nitrogen or argon or vacuum to detect a possible reaction of the to avoid formed silicon with atmospheric oxygen.

The Beam direction of the electromagnetic radiation can in principle be chosen arbitrarily, as long as a sufficient warming of the starting material until the melt takes place.

The attached figure shows schematically a device for a preferred embodiment according to the invention, the device being also an object of the invention forms.

According to the in the figure shown preferred embodiment, the thermal Reduction of the starting material in connection with a purification be carried out according to the principle of the zone melting process.

in this connection a zone of the material body to be cleaned is melted and the Melting zone through the material body guided. The impurities accumulate in the advancing enamel front at. Zone melting can be performed horizontally or vertically.

For the implementation of the Zone melting is the reaction product, which consists essentially of silicon consists, melted zone by zone with the help of microwave radiation.

silicon itself can not be directly excited by microwaves and thus heated become. Because the silicon is directly affected by the microwave radiation not heated enough In this case, a container is used which consists of a Material is made by the frequency of the electromagnetic Radiation of the microwave oven used excited and heated becomes. The warming and the melting of the silicon takes place here by heat conduction from the container wall in the silicon. The container material is therefore in view of the working frequency of the microwave oven used vote. examples for suitable container materials for commercial microwave ovens are graphite, silicon carbide etc. These materials show Excitation with electromagnetic radiation of about 2.455 GHz from commercially available microwave ovens a high energy intake, and thus a corresponding warming of the Silicon.

Of the Area of radiation or heat input and thus the The melt front can be vertical, that is perpendicular to the surface of the obtained Reaction product, or horizontally, that is parallel to the surface of the obtained reaction product, be performed.

So that the melt front can be guided in the desired direction, are means for guiding the radiation front 4 intended. For example, the corresponding microwave sources or the container 2 or both, the container 2 and the microwave sources to be made movable. Advantageously, the microwave sources are positioned so that the field maxima of the radiated microwaves are generated in the regions to be heated of the reaction product.

According to a preferred embodiment, the container 2 designed to be movable both in the vertical and in the horizontal direction.

In the figure is an example of an arrangement for a vertical zone melting process according to the invention.

To perform the zone melting here is the container 2 exposed to the reaction product side of the electromagnetic radiation.

The direction of movement of the radiation front 4 or the container 2 for the zone melting process is shown schematically by arrows.

If the conversion to silicon is combined with a zone melting process, it has proved to be advantageous to melt the silica-based starting material and react it with the reducing agent to form a separate radiation source 3 use, which radiates from above, or from below, on the starting material.

According to the invention preferred is, if necessary, appropriately doped, crushed quartz glass, with the also finely ground reducing agent and mixed in a container where.

Of the container can be in a commercial Microwave are placed and there by irradiation the starting material melted and reacted with the reducing agent to silicon become.

According to the invention can ever according to embodiment also a plurality of preferably movably arranged container be introduced simultaneously in the microwave oven.

With the method according to the invention can be based on commercial Microwave ovens by reductive conversion of pure silicon to simple Fashion and energy favorable be won.

1

microwave oven

2

Container for Inclusion of the starting material and reducing agent

3

radiation source to melt

4

radiation front for zone melting

↕

movement direction of the container and / or the radiation front for zone melting

Claims (11)

Process for the production of silicon by thermal Reduction of a silica-based starting material with a Reducing agent in a microwave oven. Method according to claim 1, characterized in that that the starting material is selected based on silica under quartz, quartz glass and doped quartz glass. Method according to claim 1 or 2, characterized that a carbon reducing agent is used. Method according to claim 3, characterized that as a reducing agent carbon powder, graphite powder or a mixture of it is used. Method according to one of the preceding claims, characterized characterized in that the silicon obtained in the microwave oven in addition one Zone melting is subjected. Device for producing silicon by thermal reduction of a silica-based starting material with a reducing agent, the device comprising a microwave oven ( 1 ) and for receiving at least one container ( 2 ) is provided, wherein microwave sources for generating a radiation front ( 4 ) are provided for performing a zone melting process. Apparatus according to claim 6, wherein the at least one container ( 2 ) is made of a material that is not transparent to the operating frequency of the microwave source used and is heated. Apparatus according to claim 6 or 7, wherein means for vertical or horizontal guidance of the radiation front ( 4 ) are provided. Apparatus according to claim 8, wherein the means are selected from at least one movably arranged microwave source, at least one movably arranged container ( 2 ) and a combination thereof for generating a mobile radiation front ( 4 ). Apparatus according to claim 9, wherein the at least one container ( 2 ) is movable in the vertical and horizontal directions. Use of a microwave oven for thermal Reduction of a silica-based starting material with a Reducing agent to silicon.